Prosthetic joint components are being installed with increasing frequency due to the enhanced stability and longevity of improved implants and surgical techniques. As a consequence, younger patients are electing joint-replacement surgery to enhance movement or alleviate pain.
In many joint-replacement situations, it is common practice to use bone-cutting guides to perform resections that correspond to the surfaces of a final implant used for fixation. In the case of primary knee-replacement surgery, for example, a stem is introduced into the distal femoral intramedullary canal to which various measurement and cutting appliances are attached.
Typically, a distal cutting guide is first installed on the stem, which is used to create a flat surface on the very end of the bone. A sizing jig is then attached in contact with this surface. Such jigs typically include adjustable feelers which touch the bone anteriorly and posteriorly, enabling the surgeon to obtain a visual indication of the correct-size implant for the patient's physiology.
Having determined the appropriate size, pins (or drill holes) are introduced into the end of the bone, and a cutting guide specifically adapted for a particular size of implant is fitted onto the pins, enabling the anterior, posterior and chamfer cuts to be performed. Typically, the location of the pins also takes into account the degree of joint rotation required, which is on the order of three degrees of external rotation for knee-replacement surgery.
Although the system just described functions adequately in most cases, it does present certain drawbacks which tend to consume time and compromise accuracy.